ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-9-2663-2009Influence of modelled soil biogenic NO emissions on related trace gases and the atmospheric oxidizing efficiencySteinkampJ.1GanzeveldL. N.2WilckeW.3LawrenceM. G.11Department of Atmospheric Chemistry, Max-Planck-Institute for Chemistry, Mainz, Germany2Department of Environmental Sciences, Chairgroup Earth System Sciences, Wageningen University and Research Centre, Wageningen, The Netherlands3Geographic Institute, Johannes Gutenberg University, Mainz, Germany230420099826632677This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/9/2663/2009/acp-9-2663-2009.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/2663/2009/acp-9-2663-2009.pdf

The emission of nitric oxide (NO) by soils (SNOx) is an important
source of oxides of nitrogen (NO<sub>x</sub>=NO+NO<sub>2</sub>) in the
troposphere, with estimates ranging from 4 to 21 Tg of nitrogen per
year. Previous studies have examined the influence of SNOx on ozone
(O<sub>3</sub>) chemistry. We employ the ECHAM5/MESSy atmospheric chemistry
model (EMAC) to go further in the reaction chain and investigate the
influence of SNOx on lower tropospheric NO<sub>x</sub>, O<sub>3</sub>,
peroxyacetyl nitrate (PAN), nitric acid (HNO<sub>3</sub>), the hydroxyl
radical (OH) and the lifetime of methane (&tau;<sub>CH<sub>4</sub></sub>). We
show that SNOx is responsible for a significant contribution to the
NO<sub>x</sub> mixing ratio in many regions, especially in the
tropics. Furthermore, the concentration of OH is substantially
increased due to SNOx, resulting in an enhanced oxidizing efficiency
of the global troposphere, reflected in a ~10% decrease in
&tau;<sub>CH<sub>4</sub></sub> due to soil NO emissions. On the other hand, in
some regions SNOx has a negative feedback on the lifetime of
NO<sub>x</sub> through O<sub>3</sub> and OH, which results in regional increases
in the mixing ratio of NO<sub>x</sub> despite lower total emissions in a
simulation without SNOx. In a sensitivity simulation in which we
reduce the other surface NO<sub>x</sub> emissions by the same amount as
SNOx, we find that they have a much weaker impact on OH and
&tau;<sub>CH<sub>4</sub></sub> and do not result in an increase in the
NO<sub>x</sub> mixing ratio anywhere.